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It showed 87.5 per cent had used cannabis, up on 84 per cent the previous year.

The proportion of positive tests showing synthetic cannabis use dropped from 4.5 per cent to 1 per cent in Rotorua.

Scion's general manager of people and performance, Keri-Anne Tane, said the company didn't carry out random testing but its drug and alcohol policy allowed it to test for drugs after accidents and on request from clients when reasonable.

She said it was important for people to stay drug free in the industry and she wasn't aware of issues relating to workers using drugs in the past.

Nationwide, positive workplace drug tests increased slightly last year on the previous one from 6.14 per cent to 6.19 per cent.

Methamphetamine showed up in 11.8 per cent of positive tests, up on 8.1 per cent in 2014.

TDDA chief executive Kirk Hardy said the methamphetamine problem was not new to New Zealand and there appeared to be a growing supply of - and demand for - methamphetamine.

Mr Hardy said there had been a decrease in the overall percentage of positive drug tests in forestry, reflecting a behavioural shift to an intolerance for drugs in such industries.

As well as preventing accidents in the workplace, the industry was addressing issues before they became a wider problem in society.

Mr Hardy said the rate of positive drug tests was also down in the transport industry.

However, the proportion of people testing positive for methamphetamine was up in both the forestry and transport industries.

Mr Hardy said that was a reflection of a national trend of methamphetamine becoming a much larger issue in New Zealand in general.

Detective Senior Sergeant Zane Smith of Rotorua CIB said despite fewer people testing positive for drugs in workplaces, staff had not noticed a drop in cannabis or methamphetamine being found during search warrants.

"We will continue to focus on and investigate persons suspected of supplying drugs because of the harm it causes in our community.

"Experience has shown us that gangs are heavily involved in the supply of drugs within Rotorua.

"There are definitely [other] organised groups who are supplying the drug, but a lot of them tend to have gang links."

Test results have shown a drop in cannabis use in the workplace, but the drug was still prevalent in the region.

"There have been several seizures of cannabis in Rotorua over the last few months and we still see the sale and use of cannabis as a significant issue for our community.

"Anecdotally, we have seen an increase in cannabis being located with several large seizures in the last month."

- Additional reporting by Kelly MakihaThe facts:

* Fewer people are testing positive for drugs at work.

* More positive tests are showing methamphetamine use.

* Fewer positive tests are showing cannabis.

* Police say cannabis and methamphetamine are still problems in Rotorua.